EP1327613B1 - Quartz glass blank for preparing an optical component and its application - Google Patents

Quartz glass blank for preparing an optical component and its application Download PDF

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Publication number
EP1327613B1
EP1327613B1 EP02027127A EP02027127A EP1327613B1 EP 1327613 B1 EP1327613 B1 EP 1327613B1 EP 02027127 A EP02027127 A EP 02027127A EP 02027127 A EP02027127 A EP 02027127A EP 1327613 B1 EP1327613 B1 EP 1327613B1
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Prior art keywords
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quartz glass
content
molecules
glass blank
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EP02027127A
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German (de)
French (fr)
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EP1327613A1 (en
Inventor
Bodo KÜHN
Bruno Dr. Uebbing
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Heraeus Quarzglas GmbH and Co KG
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Heraeus Quarzglas GmbH and Co KG
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    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B19/00—Other methods of shaping glass
    • C03B19/14—Other methods of shaping glass by gas- or vapour- phase reaction processes
    • C03B19/1453—Thermal after-treatment of the shaped article, e.g. dehydrating, consolidating, sintering
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C4/00—Compositions for glass with special properties
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B19/00—Other methods of shaping glass
    • C03B19/14—Other methods of shaping glass by gas- or vapour- phase reaction processes
    • C03B19/1415—Reactant delivery systems
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C3/00—Glass compositions
    • C03C3/04—Glass compositions containing silica
    • C03C3/06—Glass compositions containing silica with more than 90% silica by weight, e.g. quartz
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B2201/00—Type of glass produced
    • C03B2201/06—Doped silica-based glasses
    • C03B2201/07—Impurity concentration specified
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B2201/00—Type of glass produced
    • C03B2201/06—Doped silica-based glasses
    • C03B2201/20—Doped silica-based glasses doped with non-metals other than boron or fluorine
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B2201/00—Type of glass produced
    • C03B2201/06—Doped silica-based glasses
    • C03B2201/20—Doped silica-based glasses doped with non-metals other than boron or fluorine
    • C03B2201/21—Doped silica-based glasses doped with non-metals other than boron or fluorine doped with molecular hydrogen
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B2201/00—Type of glass produced
    • C03B2201/06—Doped silica-based glasses
    • C03B2201/20—Doped silica-based glasses doped with non-metals other than boron or fluorine
    • C03B2201/23—Doped silica-based glasses doped with non-metals other than boron or fluorine doped with hydroxyl groups
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C2201/00—Glass compositions
    • C03C2201/06—Doped silica-based glasses
    • C03C2201/08—Doped silica-based glasses containing boron or halide
    • C03C2201/11—Doped silica-based glasses containing boron or halide containing chlorine
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C2201/00—Glass compositions
    • C03C2201/06—Doped silica-based glasses
    • C03C2201/20—Doped silica-based glasses containing non-metals other than boron or halide
    • C03C2201/21—Doped silica-based glasses containing non-metals other than boron or halide containing molecular hydrogen
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C2201/00—Glass compositions
    • C03C2201/06—Doped silica-based glasses
    • C03C2201/20—Doped silica-based glasses containing non-metals other than boron or halide
    • C03C2201/23—Doped silica-based glasses containing non-metals other than boron or halide containing hydroxyl groups
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C2203/00—Production processes
    • C03C2203/40—Gas-phase processes
    • C03C2203/42—Gas-phase processes using silicon halides as starting materials
    • C03C2203/44—Gas-phase processes using silicon halides as starting materials chlorine containing
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C2203/00—Production processes
    • C03C2203/50—After-treatment
    • C03C2203/52—Heat-treatment

Definitions

  • the present invention relates to a quartz glass blank for an optical component for transmission Ultraviolet radiation of a wavelength of 250 nm and shorter.
  • the invention relates to a use of a quartz glass blank for the production a component for use in microlithography in conjunction with ultraviolet radiation a wavelength of 250 nm and shorter.
  • Quartz glass optical components become more energetic, ultraviolet, especially for transmission Laser radiation, for example as optical fibers or in the form of exposure optics in microlithography devices for the production of highly integrated circuits in semiconductor chips used.
  • the exposure systems of modern microlithography devices are equipped with excimer lasers equipped, the high-energy, pulsed UV radiation of a wavelength of 248 nm (KrF laser) or from 193 nm (ArF laser).
  • Short-wave UV radiation can be defective in optical components made of synthetic quartz glass generate, which lead to absorptions.
  • irradiation conditions depend on type and Extent of defect formation and the induced absorption by the quality of the respective Quartz glass, essentially due to structural properties, such as density, Refractive index and homogeneity and is determined by the chemical composition.
  • the number of induced structural defects and the absorption induced thereby are So depending on the number of applied laser pulses and their energy density and of Material factors.
  • EP-A1 401 845 describes processes for producing synthetic quartz glass by flame hydrolysis of silicon-containing compounds. These can be distinguished on the basis of the starting substances and the manner of glazing the deposited SiO 2 particles.
  • a frequently used starting material in the production of synthetic quartz glass by flame hydrolysis is SiCl 4 .
  • other, for example, chlorine-free silicon-containing organic compounds are used, such as silanes or siloxanes.
  • SiO 2 particles are deposited in layers on a rotating substrate. At a sufficiently high temperature on the surface of the substrate, there is an immediate vitrification of the SiO 2 particles ("direct glazing").
  • EP-A 401 845 an annealing program is proposed in which the blank of a 50-hour Holding time is subjected to a temperature of about 1100 ° C and finally in a slow cooling step with a cooling rate of 2 ° / h to 900 ° C and then in the closed Oven is cooled to room temperature. At this temperature treatment it can by Discharge of components - especially hydrogen - to local changes the chemical composition and to a concentration gradient of the near-surface Areas of the blank come inside. To improve the radiation resistance of the quartz glass due to the defect-healing effect of hydrogen is in EP-A1 401 845 recommended, the annealed quartz glass blank subsequently with hydrogen to be loaded by treating this at elevated temperature in a hydrogen-containing atmosphere becomes.
  • quartz glass UV radiation causes only a comparatively low absorption increase, so that this quartz glass in this respect by a high resistance to short-wave UV radiation distinguishes.
  • other damage mechanisms be effective, for example, in the generation of fluorescence or in can show a change in the refractive index.
  • a well-known phenomenon in this context is the so-called "compaction” which occurs during or after laser irradiation with high energy density. This effect manifests itself in a local density increase, which leads to an increase in the refractive index and thus to a deterioration of the imaging properties of the optical component.
  • an opposite effect may also occur if a quartz glass optical component is exposed to laser radiation of low energy density but high number of pulses. Under these conditions, a so-called “decompacting” is observed (also referred to in the Anglo-Saxon literature as "rarefaction”), which is accompanied by a decrease in the refractive index. This leads to a deterioration of the imaging properties. This damage mechanism is described by CK Van Peski, R. Morton and Z.
  • Compaction and decompression are thus defects that are not necessarily in one Increase in the radiation-induced absorption outer, but the life of an optical Can limit component.
  • the present invention is therefore based on the object, a blank made of synthetic Quartz glass for an optical component for the transmission of ultraviolet radiation of one wavelength of 250 nm and shorter, which has a low induced absorption and which is simultaneously optimized for compaction and decompression. Still lies
  • the invention has for its object to provide a suitable use for it.
  • a glass structure that is substantially free of oxygen deficiency sites is understood to be a glass structure in which the concentrations of oxygen deficiency defects and oxygen excess defects are below the detectability limit of the Shelby method.
  • This detection method is published in "Reaction of hydrogen with hydroxyl-free vitreous silica” (J. Appl. Phys., Vol. 51, No. 5 (May 1980), pp. 2589-2593). Quantitatively, this results in a number of oxygen deficiency defects or oxygen excess defects in the glass structure of not more than about 10 17 per gram of fused silica.
  • the stated components are above the volume of the optical component equally distributed.
  • the stated concentration data here refer to the optical used area of the component.
  • the OH content is determined by measuring the IR absorption by the method of DM Dodd et al. ("Optical Determinations of OH in Fused Silica", J. Appl. Physics (1966), p. 3911).
  • the H 2 content is determined by means of a Raman measurement, which was first described by Khotimchenko et al. Zhurnal Prikladnoi Spectroscopy, Vol. 46, No. 6 (June 1987), pp. 987-991) has been proposed ("Determining the Content of Hydrogen Dissolved in Quartz Glass Using the Methods of Raman Scattering and Mass Spectrometry").
  • the content of SiH groups is determined by means of Raman spectroscopy, wherein a calibration is carried out by means of a chemical reaction with hydrogen: Si-O-Si + H 2 ⁇ Si-H + Si-OH, as described in Shelby "Reaction of hydrogen with hydroxyl-free vitreous silica” (J. Appl. Phys., Vol. 51, No. 5 (May 1980) , Pp. 2589-2593).
  • the chlorine content of the silica glass is determined chemically by precipitation of chlorine as silver chloride or using an ion-selective electrode.
  • the inhomogeneity of the refractive index ⁇ n becomes interferometric at a wavelength of 633 nm (He-Ne laser), where ⁇ n is the difference between the maximum value and the Minimum value of the refractive index distribution, measured over the optically used surface area, also CA area ("clear aperture") called.
  • the CA range is given by Projection of the irradiated volume on a plane perpendicular to the direction of transmission.
  • the stress birefringence is interferometrically at a wavelength of 633 nm (He-Ne laser) according to the "Measurement of the Residual Birefringence Distribution in Glass Laser Disk by Transverse Zeeman Laser "(Electronics and Communications in Japan, Part 2, Vol. No. 5, 1991; (translated from Denshi Joho Tsushin Gakkai Ronbunshi Vol. 73-C-I, No. 10, 1990) pp. 652-657).
  • the quartz glass, from which the blank according to the invention consists, inter alia, by relatively high H 2 - and OH contents on the one hand and by a chlorine content with a comparatively narrow concentration range between 60 wt ppm and 120 wt ppm on the other hand.
  • Such quartz glass is not easily produced by means of the "soot method" described above.
  • the soot method is usually quartz glass having an OH content in the range of a few ppm by weight to 200 ppm by weight, the H 2 content due to the temperature treatments during vitrification and homogenization of the quartz glass is typically below the detection limit.
  • OH contents of 450 to 1200 ppm by weight and H 2 contents of 1 x 10 18 molecules / cm 3 are typical. It has surprisingly been found that in such a quartz glass chlorine has a favorable effect on the radiation resistance, when the chlorine is present in a narrow concentration range between 60 ppm by weight to 120 ppm by weight.
  • the RDP-leading damage mechanism is particularly pronounced at H 2 contents of more than 2.0 x 10 18 molecules / cm 3 .
  • H 2 contents of more than 2.0 x 10 18 molecules / cm 3 Whereas at an H 2 content of less than 3 x 10 17 molecules / cm 3, the above-mentioned defect-healing effect of hydrogen over short-wave UV radiation with energy densities of more than 0.05 mJ / cm 2 is so low that it is during the Proper use of the optical component to intolerable transmission losses comes.
  • the quartz glass in the blank according to the invention both in Hinbiick on Optimized compaction as well as decompaction, and at the same time it has a low induced Absorption against short-wave UV radiation.
  • An OH content in this range represents a preferred compromise between decompaction and compaction on the one hand and RDP on the other hand, if the quartz glass is to be used with UV radiation with energy densities of more than 0.05 mJ / cm 2 .
  • the H 2 content is advantageously in the range of 5 ⁇ 10 17 molecules / cm 3 to 1 ⁇ 10 18 molecules / cm 3 .
  • both the favorable, defect-curing effect of the hydrogen is present in a particularly high degree, and at the same time decompaction is largely avoided.
  • the quartz glass blank has a chlorine content in the range of 80 ppm by weight to 100 ppm by weight. With a chlorine content within this narrow concentration range, a low decompaction and induced absorption is achieved, in particular when the quartz glass blank is used in conjunction with UV radiation of high energy densities of more than 0.05 mJ / cm 2 .
  • Design rule (2) gives a minimum concentration of hydrogen depending on the irradiation conditions (pulse energy density and pulse rate), below which the defect-healing effect of hydrogen is so low that it is during the intended use of the optical component to intolerable Transmission losses comes.
  • Dimensioning rule (3) defines an upper limit Hydrogen as a function of the pulse energy density, above the increased RDP or decompacting occurs.
  • the indicated hydrogen concentrations refer in each case on the optically used area within the quartz glass blank (CA area). Usually this is the central area of the building part or of the quartz glass blank.
  • the design rule (4) gives an OH content of 513 ppm by weight.
  • the design rule (4) has proved to be particularly suitable for the determination of the OH content with regard to low compaction and at the same time low decompaction if the pulse energy density is less than 0.3 mJ / cm 2 , preferably less than 0.15 mJ / cm 2 , is.
  • the OH content C OH in ppm by weight (indicated in the figure as “OH content”) is plotted against the pulse energy density ⁇ in mJ / cm 2 (indicated in the figure as “energy density”).
  • the drawn curve is based on damage measurements with different qualities of quartz glass, which differ in their OH content. The measurement takes place under laser radiation of a wavelength of 193 nm and at a laser pulse length between 20 and 50 nanoseconds. The laser pulse length is determined according to V. Liberman, M. Rothschild, JHC Sedlacek, RS Tamilo, A.
  • the OH content which a quartz glass must have, so that it exhibits neither compaction nor decompaction can be selected from the curve or formula (4).
  • Table 1 shows the results of irradiation measurements on quartz glass blanks different chemical composition and under different irradiation conditions. In the last three columns of the table is given qualitatively, whether the respective blank compacting, Decompacting or induced absorption shows.
  • the properties mentioned in columns 2 to 8 are each determined on a cylindrical quartz glass blank having an outer diameter of 240 mm and a thickness of 60 mm. These are lens blanks for a microlithography device that uses excimer laser radiation with a wavelength of 193 nm. Apart from a small excess, which is still removed in the manufacture of the lens, the blank dimensions also correspond to the lens dimensions.
  • the quartz glass volume corresponding to the CA region of the lens obtained therefrom is determined here by the circular area of the lens, minus an edge of a few millimeters for the lens frame, and the thickness.
  • the oxygen defect site concentration is indicated, in the column “ ⁇ n” the refractive index difference determined over the CA region, and in the column “ ⁇ ” the maximum birefringence determined in the CA region.
  • rod-shaped samples with a dimension of 25 ⁇ 25 ⁇ 200 mm 3 were removed from the respective quartz glass blanks and prepared in the same manner (polishing of the opposite 25 ⁇ 25 mm 2 surfaces).
  • compaction and decompaction were determined by with a commercial interferometer (Zygo GPI-XP) at a wavelength of 633nm, the relative increase or decrease of the refractive index in the irradiated area in comparison to the unirradiated area was measured.
  • the quartz glass blanks are designed for the production of optical lenses for a microlithography device for use with UV radiation of a wavelength of 193 nm, wherein the optical component during its intended use typically a radiation having an energy density of about 0.1 mJ / cm 2 is suspended.
  • Typical pulse numbers are between 10 11 and 10 12 .
  • Blanks 1 to 4 according to Table 1 were prepared as follows: These are quartz glasses produced by the direct glazing process. On a disc-shaped, rotating about its central axis substrate is finely divided SiO 2 by means of a detonating gas burner, which is directly vitrified by the heat of the oxyhydrogen flame to form a rod-shaped quartz glass blank. The hydrogen content in this process stage is still about 2 ⁇ 10 18 molecules / cm 3 .
  • the blanks 1 to 4 differ only in the respective chlorine contents.
  • the CI content is adjusted by setting the flow rates for H 2 , O 2 and SiCl 4 .
  • design rule (4) sets the OH content to be set in conjunction with the typical feed pulse energy density of about 0.1 mJ / cm 2 .
  • the hydrogen content is determined by the design rules (2) and (3), as it is to be set in connection with the typical application pulse energy density of about 0.1 mJ / cm 2 .
  • the setting of the predetermined H 2 content is carried out by annealing the blanks at 1100 ° C.
  • this rule of thumb gives a minimum H 2 content to be set in the quartz glass, depending on the number of pulses between 1 ⁇ 10 17 molecules / cm 3 and 10 ⁇ 10 17 molecules / cm 3 - and a maximum H 2 content of 2 ⁇ 10 18 molecules / cm 3 .
  • the quartz glass blank is then clamped in a quartz glass lathe, heated zone by zone to a temperature of about 2000 ° C and thereby twisted.
  • a quartz glass lathe heated zone by zone to a temperature of about 2000 ° C and thereby twisted.
  • One for that suitable homogenization method is described in EP-A1 673 888. After several times Twisting is a quartz glass body in the form of a round rod with a diameter of 80 mm and a length of about 800 mm, which is free of streaks in three directions.
  • a circular quartz glass cylinder having an outer diameter of 240 mm and a length of 80 mm is formed therefrom.
  • the quartz glass cylinder is heated to 1100 ° C. under air and atmospheric pressure and then cooled to 900 ° C. at a cooling rate of 2 ° C./h, only (in the CA range) a stress birefringence of not more than 2 is obtained nm / cm, and the refractive index distribution is so homogeneous that the difference between the maximum value and the minimum value is less than 2 ⁇ 10 -6 .
  • a rod-shaped sample with a dimension of 25 ⁇ 25 ⁇ 200 mm 3 is taken, which has an H 2 content of about 1 ⁇ 10 18 molecules / cm 3 and about 700 ppm by weight OH.
  • the production of the blanks 5 to 7 takes place as that of the blanks 1-4 by varying the flow rates of the individual media.
  • the H 2 content of the resulting blanks is adjusted by selecting the length of the annealing program and taking into account the diffusion of the annealing of the hot-formed quartz glass cylinder.
  • Blanks 1, 5 and 7 show the best results at energy densities of 0.1 0.2 and 0.05 mJ / cm 2, respectively.
  • Blank 2 shows under the action of ultraviolet radiation with a relatively high energy density of 0.3 mJ / cm 2 compaction, which depending on the application can be tolerated within limits.

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Abstract

Quartz glass blank has a glass structure without oxygen defect sites, a hydrogen content of 3 x 1017 to 2.0 x 1018 molecules/cm3, a hydroxyl content of 500-1000 wt. ppm, a silicon hydrogen group content of less than 2 x 1017 molecules/cm3, a chlorine content of 60-120 wt. ppm, an inhomogenity in refractive index DELTAn of less than 2 ppm and voltage birefringence of less than 2 nm/cm. Preferred Features: The hydroxyl (OH) content is 600-900, preferably 750-950 wt. ppm. The hydrogen content is 5 x 1017 to 1.0 x 1018 molecules/cm3. The chlorine content is 80-100 wt. ppm.

Description

Die vorliegende Erfindung betrifft einen Quarzglasrohling für ein optisches Bauteil zur Übertragung ultravioletter Strahlung einer Wellenlänge von 250 nm und kürzer.The present invention relates to a quartz glass blank for an optical component for transmission Ultraviolet radiation of a wavelength of 250 nm and shorter.

Weiterhin betrifft die Erfindung eine Verwendung eines Quarzglasrohlings für die Herstellung eines Bauteils für den Einsatz in der Mikrolithographie in Verbindung mit ultravioletter Strahlung einer Wellenlänge von 250 nm und kürzer.Furthermore, the invention relates to a use of a quartz glass blank for the production a component for use in microlithography in conjunction with ultraviolet radiation a wavelength of 250 nm and shorter.

Optische Bauteile aus Quarzglas werden insbesondere für die Übertragung energiereicher, ultravioletter Laserstrahlung beispielsweise als optische Fasern oder in Form von Belichtungsoptiken in Mikrolithographiegeräten für die Herstellung hochintegrierter Schaltungen in Halbleiterchips eingesetzt. Die Belichtungssysteme modemer Mikrolithographiegeräte sind mit Excimerlasern bestückt, die energiereiche, gepulste UV-Strahlung einer Wellenlänge von 248 nm (KrF-Laser) oder von 193 nm (ArF-Laser) abgeben.Quartz glass optical components become more energetic, ultraviolet, especially for transmission Laser radiation, for example as optical fibers or in the form of exposure optics in microlithography devices for the production of highly integrated circuits in semiconductor chips used. The exposure systems of modern microlithography devices are equipped with excimer lasers equipped, the high-energy, pulsed UV radiation of a wavelength of 248 nm (KrF laser) or from 193 nm (ArF laser).

Kurzwellige UV-Strahlung kann in optischen Bauteilen aus synthetischem Quarzglas Defekte erzeugen, die zu Absorptionen führen. Neben den Bestrahlungsbedingungen hängen Art und Ausmaß einer Defektbildung und der dadurch induzierten Absorption von der Qualität des jeweiligen Quarzglases ab, die im wesentlichen durch strukturelle Eigenschaften, wie Dichte, Brechzahlverlauf und Homogenität und von der chemischen Zusammensetzung bestimmt wird.Short-wave UV radiation can be defective in optical components made of synthetic quartz glass generate, which lead to absorptions. In addition to the irradiation conditions depend on type and Extent of defect formation and the induced absorption by the quality of the respective Quartz glass, essentially due to structural properties, such as density, Refractive index and homogeneity and is determined by the chemical composition.

Eine modellhafte Formel drückt diesen Zusammenhang zwischen den Bestrahlungsbedingungen, den Materialfaktoren und der induzierten Absorption αin folgendermaßen aus: αin = a x ε b x P wobei a und b Materialfaktoren sind und ε und P für die Energiedichte bzw. die Pulszahl stehen.A model formula expresses this relationship between the irradiation conditions, the material factors and the induced absorption α in the following way: α in = ax ε b x P where a and b are material factors and ε and P stand for the energy density and the pulse number.

Die Anzahl der induzierten strukturellen Defekte und die dadurch induzierte Absorption sind also abhängig von der Anzahl der einwirkenden Laserpulse und deren Energiedichte sowie von Materialfaktoren.The number of induced structural defects and the absorption induced thereby are So depending on the number of applied laser pulses and their energy density and of Material factors.

Der Einfluß der chemischen Zusammensetzung des Quarzglases auf das Schädigungsverhalten bei der Bestrahlung mit energiereichem UV-Licht ist beispielsweise in der EP-A1 401 845 beschrieben. Eine hohe Strahlenbeständigkeit ergibt sich demnach bei einem Quarzglas, das sich durch hohe Reinheit, einen OH-Gehalt im Bereich von 100 bis ca. 1000 Gew-ppm und gleichzeitig durch eine Wasserstoffkonzentration von mindestens 5x1016 Molekülen pro cm3 (bezogen auf das Volumen des Quarzglases) auszeichnet. Weiterhin weist das bekannte synthetische Quarzglas eine Spannungsdoppelbrechung von weniger als 5 nm/cm auf, und es ist weitgehend frei von Sauerstoffdefektstellen.The influence of the chemical composition of the quartz glass on the damage behavior during the irradiation with high-energy UV light is described for example in EP-A1 401 845. A high radiation resistance is thus obtained in the case of a quartz glass which is characterized by high purity, an OH content in the range from 100 to about 1000 ppm by weight and at the same time by a hydrogen concentration of at least 5 × 10 16 molecules per cm 3 (based on the volume of the Quartz glass). Furthermore, the known synthetic quartz glass has a stress birefringence of less than 5 nm / cm, and it is largely free of oxygen defect sites.

In der EP-A1 401 845 werden außerdem Verfahren zur Herstellung von synthetischem Quarzglas durch Flammenhydrolyse siliciumhaltiger Verbindungen beschrieben. Diese lassen sich anhand der Ausgangssubstanzen und der Art und Weise der Verglasung der abgeschiedenen SiO2-Partikel unterscheiden. Eine häufig eingesetzte Ausgangssubstanz bei der Herstellung von synthetischem Quarzglas durch Flammenhydrolyse ist SiCl4. Es werden aber auch andere, beispielsweise chlorfreie siliziumhaltige organische Verbindungen verwendet, wie Silane oder Siloxane. In jedem Fall werden auf einem rotierenden Substrat SiO2-Partikel schichtweise abgeschieden. Bei hinreichend hoher Temperatur auf der Oberfläche des Substrats kommt es zu einem unmittelbaren Verglasen der SiO2-Partikel ("Direktverglasen"). Im Unterschied dazu wird bei dem sogenannten "Sootverfahren" die Temperatur während der Abscheidung der SiO2-Partikel so niedrig gehalten, dass ein poröser Sootkörper gebildet wird, bei dem SiO2-Partikel nicht oder wenig verglast sind. Das Verglasen unter Bildung von Quarzglas erfolgt beim Sootverfahren durch nachträgliches Sintern des Sootkörpers. Beide Herstellungsverfahren führen zu einem dichten, transparenten, hochreinen Quarzglas, wobei die Herstellungskosten beim Sootverfahren niedriger sind als beim Direktverglasen.In addition, EP-A1 401 845 describes processes for producing synthetic quartz glass by flame hydrolysis of silicon-containing compounds. These can be distinguished on the basis of the starting substances and the manner of glazing the deposited SiO 2 particles. A frequently used starting material in the production of synthetic quartz glass by flame hydrolysis is SiCl 4 . However, other, for example, chlorine-free silicon-containing organic compounds are used, such as silanes or siloxanes. In any case, SiO 2 particles are deposited in layers on a rotating substrate. At a sufficiently high temperature on the surface of the substrate, there is an immediate vitrification of the SiO 2 particles ("direct glazing"). In contrast, in the so-called "soot method", the temperature during the deposition of the SiO 2 particles is kept so low that a porous soot body is formed in which SiO 2 particles are not or little glazed. The vitrification with formation of quartz glass takes place during the soot process by subsequent sintering of the soot body. Both manufacturing processes result in a dense, transparent, high-purity quartz glass, the production costs being lower in the soot process than in direct glazing.

Um mechanische Spannungen innerhalb des Rohlings abzubauen und um eine homogene Verteilung der fiktiven Temperatur zu erreichen, wird dieser üblicherweise getempert. In der EP-A 401 845 wird ein Temperprogramm vorgeschlagen, bei dem der Rohling einer 50-stündigen Haltezeit bei einer Temperatur von etwa 1100 °C unterzogen wird und abschließend in einem langsamen Abkühlschritt mit einer Abkühlrate von 2 °/h auf 900 °C und dann im geschlossenen Ofen auf Raumtemperatur abgekühlt wird. Bei dieser Temperaturbehandlung kann es durch Ausdiffusion von Komponenten - insbesondere von Wasserstoff - zu lokalen Veränderungen der chemischen Zusammensetzung und zu einem Konzentrationsgradienten von den oberflächennahen Bereichen des Rohlings nach Innen kommen. Zur Verbesserung der Strahlenbeständigkeit des Quarzglases infolge der defektausheilenden Wirkung von Wasserstoff wird in der EP-A1 401 845 empfohlen, den getemperten Quarzglas-Rohling nachträglich mit Wasserstoff zu beladen, indem dieser bei erhöhter Temperatur in wasserstoffhaltiger Atmosphäre behandelt wird.To reduce mechanical stresses within the blank and to a homogeneous To achieve distribution of the fictitious temperature, this is usually tempered. In EP-A 401 845 an annealing program is proposed in which the blank of a 50-hour Holding time is subjected to a temperature of about 1100 ° C and finally in a slow cooling step with a cooling rate of 2 ° / h to 900 ° C and then in the closed Oven is cooled to room temperature. At this temperature treatment it can by Discharge of components - especially hydrogen - to local changes the chemical composition and to a concentration gradient of the near-surface Areas of the blank come inside. To improve the radiation resistance of the quartz glass due to the defect-healing effect of hydrogen is in EP-A1 401 845 recommended, the annealed quartz glass blank subsequently with hydrogen to be loaded by treating this at elevated temperature in a hydrogen-containing atmosphere becomes.

In der Literatur sind eine Vielzahl von Schädigungsmustem beschrieben, bei denen es bei andauemder UV-Bestrahlung zu einem Anstieg der Absorption kommt. Die induzierte Absorption kann zum Beispiel linear ansteigen, oder es wird nach einem anfänglichen Anstieg eine Sättigung erreicht. Weiterhin wird beobachtet, dass eine anfänglich registrierte Absorptionsbande zunächst wenige Minuten nach Abschalten des Lasers verschwindet, sich aber nach erneuter Bestrahlung schnell wieder auf dem einmal erreichten Niveau wiederherstellt. Dieses Verhalten wird als "rapid-damage-process" (RDP) bezeichnet. Hintergrund diesen Verhaltens ist, dass Wasserstoffmoleküle die Netzwerkdefekte im Quarzglas absättigen, wobei aber die Stabilität der Bindungen an den Defektstellen gering ist, so dass sie erneut aufbrechen, wenn das Bauteil wieder bestrahlt wird. Es ist auch ein Schädigungsverhalten bekannt, bei dem sich strukturelle Defekte offenbar derart kumulieren, dass sie sich in einer plötzlichen, starken Zunahme der Absorption äußern. Der starke Anstieg der Absorption bei dem zuletzt beschriebenen Schädigungsverhalten wird in der Literatur als SAT-Effekt bezeichnet.In the literature, a variety of damage patterns are described in which it andauemder UV irradiation leads to an increase in absorption. The induced absorption For example, it may increase linearly, or saturate after an initial increase reached. Furthermore, it is observed that an initially registered absorption band first a few minutes after switching off the laser disappears, but after renewed Radiation quickly restored to the level once reached. This behavior is called "rapid-damage-process" (RDP). Background of this behavior is that Hydrogen molecules saturate the network defects in the quartz glass, but the stability the bonds at the defect sites is small, allowing them to break open again when the component is irradiated again. It is also known a damage behavior in which structural Defects apparently accumulate in such a way that they result in a sudden, strong increase of the Express absorption. The strong increase in absorption in the last-mentioned damage behavior is referred to in the literature as the SAT effect.

Bei dem aus der EP-A1 401 845 bekannten Quarzglas verursacht UV-Strahlung nur eine vergleichsweise geringe Absorptionszunahme, so dass sich dieses Quarzglas insoweit durch eine hohe Beständigkeit gegenüber kurzwelliger UV-Strahlung auszeichnet. Jedoch können neben dem Auftreten von Absorption bzw. reduzierter Transmission auch andere Schädigungsmechanismen wirksam werden, die sich beispielsweise in der Generierung von Fluoreszenz oder in einer Veränderung des Brechungsindex zeigen können.In the known from EP-A1 401 845 quartz glass UV radiation causes only a comparatively low absorption increase, so that this quartz glass in this respect by a high resistance to short-wave UV radiation distinguishes. However, besides the occurrence of absorption or reduced transmission also other damage mechanisms be effective, for example, in the generation of fluorescence or in can show a change in the refractive index.

Ein bekanntes Phänomen in diesem Zusammenhang ist die sogenannte "Kompaktierung", die während bzw. nach Laser-Bestrahlung mit hoher Energiedichte auftritt. Dieser Effekt äußerst sich in einer lokalen Dichteerhöhung, die zu einem Anstieg des Brechungsindex und damit zu einer Verschlechterung der Abbildungseigenschaften des optischen Bauteils führt.
Ein gegenteiliger Effekt kann jedoch ebenso auftreten, wenn ein optisches Bauteil aus Quarzglas einer Laserstrahlung geringer Energiedichte aber hoher Pulszahl ausgesetzt wird. Unter diesen Bedingungen wird eine sogenannte "Dekompaktierung" beobachtet (in der angelsächsischen Literatur auch als "rarefaction" bezeichnet), die mit einer Erniedrigung des Brechungsindex einhergeht. Dies führt zu einer Verschlechterung der Abbildungseigenschaften. Dieser Schädigungsmechanismus ist beschrieben von C. K. Van Peski, R. Morton und Z. Bor ("Behaviour of fused silica irradiated by low level 193 nm excimer laser for tens of billions of pulses", J. Non-Cryst. Solids 265 (2000) S.285-289).A well-known phenomenon in this context is the so-called "compaction" which occurs during or after laser irradiation with high energy density. This effect manifests itself in a local density increase, which leads to an increase in the refractive index and thus to a deterioration of the imaging properties of the optical component.
However, an opposite effect may also occur if a quartz glass optical component is exposed to laser radiation of low energy density but high number of pulses. Under these conditions, a so-called "decompacting" is observed (also referred to in the Anglo-Saxon literature as "rarefaction"), which is accompanied by a decrease in the refractive index. This leads to a deterioration of the imaging properties. This damage mechanism is described by CK Van Peski, R. Morton and Z. Bor ("Behavior of fused silica irradiated by low level 193 nm excimer laser for tens of billions of pulses", J. Non-Cryst., Solids 265 (2000) p .285-289).

Kompaktierung und Dekompaktierung sind somit Defekte, die sich nicht zwangsläufig in einer Zunahme der strahlungsinduzierten Absorption äußeren, die aber die Lebensdauer eines optischen Bauteils begrenzen können.Compaction and decompression are thus defects that are not necessarily in one Increase in the radiation-induced absorption outer, but the life of an optical Can limit component.

Der vorliegenden Erfindung liegt daher die Aufgabe zugrunde, einen Rohling aus synthetischem Quarzglas für ein optisches Bauteil für die Übertragung ultravioletter Strahlung einer Wellenlänge von 250 nm und kürzer bereitzustellen, das eine geringe induzierte Absorption aufweist und das gleichzeitig hinsichtlich Kompaktierung und Dekompaktierung optimiert ist. Weiterhin liegt der Erfindung die Aufgabe zugrunde, eine geeignete Verwendung dafür anzugeben.The present invention is therefore based on the object, a blank made of synthetic Quartz glass for an optical component for the transmission of ultraviolet radiation of one wavelength of 250 nm and shorter, which has a low induced absorption and which is simultaneously optimized for compaction and decompression. Still lies The invention has for its object to provide a suitable use for it.

Hinsichtlich des Rohlings wird diese Aufgabe erfindungsgemäß durch eine Ausführungsform eines Quarzglas-Rohlings gelöst, der die Kombination folgender Eigenschaften aufweist:

  • eine Glasstruktur im wesentlichen ohne Sauerstoffdefektstellen,
  • einen H2-Gehalt im Bereich von 3 x 1017 Molekülen/cm3 bis 2,0 x 1018 Molekülen/cm3,
  • einem OH-Gehalt im Bereich von 500 Gew-ppm bis 1000 Gew-ppm,
  • einem Gehalt an SiH-Gruppen von weniger als 2 x 1017 Moleküle/cm3
  • einem Chlorgehalt im Bereich von 60 Gew-ppm bis 120 Gew-ppm,
  • einer Inhomogenität im Brechungsindex Δn von weniger als 2 ppm und
  • einer Spannungsdoppelbrechung von weniger als 2 nm/cm.
With regard to the blank, this object is achieved according to the invention by an embodiment of a quartz glass blank, which has the combination of the following properties:
  • a glass structure essentially without oxygen defect sites,
  • an H 2 content in the range from 3 × 10 17 molecules / cm 3 to 2.0 × 10 18 molecules / cm 3 ,
  • an OH content in the range from 500 ppm by weight to 1000 ppm by weight,
  • a content of SiH groups of less than 2 x 10 17 molecules / cm 3
  • a chlorine content in the range of 60 ppm by weight to 120 ppm by weight,
  • an inhomogeneity in the refractive index Δn of less than 2 ppm and
  • a stress birefringence of less than 2 nm / cm.

Unter einer Glasstruktur, die im wesentlichen frei von Sauerstoffdefektstellen ist, wird hier eine Glasstruktur verstanden, bei der die Konzentrationen von Sauerstoff-Unterschussdefekten und von Sauerstoff-Überschussdefekten unterhalb der Nachweisbarkeitsgrenze der Methode von Shelby liegen. Diese Nachweis-Methode ist veröffentlicht in "Reaction of hydrogen with hydroxyl-free vitreous silica" (J. Appl. Phys., Vol. 51, No. 5 (Mai 1980), S. 2589-2593). Quantitativ ergibt sich dabei eine Anzahl an Sauerstoff-Unterschussdefekten oder an Sauerstoff-Überschussdefekten in der Glasstruktur von nicht mehr als etwa 1017 pro Gramm Quarzglas.A glass structure that is substantially free of oxygen deficiency sites is understood to be a glass structure in which the concentrations of oxygen deficiency defects and oxygen excess defects are below the detectability limit of the Shelby method. This detection method is published in "Reaction of hydrogen with hydroxyl-free vitreous silica" (J. Appl. Phys., Vol. 51, No. 5 (May 1980), pp. 2589-2593). Quantitatively, this results in a number of oxygen deficiency defects or oxygen excess defects in the glass structure of not more than about 10 17 per gram of fused silica.

Idealerweise sind die angegebenen Komponenten über das Volumen des optischen Bauteils gleichmäßig verteilt. Die genannten Konzentrationsangaben beziehen sich hier auf den optisch genutzten Bereich des Bauteils .Ideally, the stated components are above the volume of the optical component equally distributed. The stated concentration data here refer to the optical used area of the component.

Der OH-Gehalt ergibt sich durch Messung der IR-Absorption nach der Methode von D. M. Dodd et al. ("Optical Determinations of OH in Fused Silica", J. Appl. Physics (1966), S. 3911). Der H2-Gehalt wird anhand einer Raman-Messung ermittelt, die erstmals von Khotimchenko et al. vorgeschlagen worden ist ("Determining the Content of Hydrogen Dissolved in Quartz Glass Using the Methods of Raman Scattering and Mass Spectrometry" Zhurnal Prikladnoi Spektroskopii, Vol. 46, No. 6 (Juni 1987), S. 987-991). Der Gehalt an SiH-Gruppen wird mittels Raman-Spektroskopie ermittelt, wobei eine Kalibrierung anhand einer chemischen Reaktion mit Wasserstoff erfolgt:
Si-O-Si + H2 → Si-H + Si-OH , wie in Shelby "Reaction of hydrogen with hydroxyl-free vitreous silica" (J. Appl. Phys., Vol. 51, No. 5 (Mai 1980), S. 2589-2593) beschrieben. Der Chlorgehalt des Quarzglases wird chemisch anhand einer Fällung von Chlor als Silberchlorid oder unter Verwendung einer ionenselektiven Elektrode ermittelt.The OH content is determined by measuring the IR absorption by the method of DM Dodd et al. ("Optical Determinations of OH in Fused Silica", J. Appl. Physics (1966), p. 3911). The H 2 content is determined by means of a Raman measurement, which was first described by Khotimchenko et al. Zhurnal Prikladnoi Spectroscopy, Vol. 46, No. 6 (June 1987), pp. 987-991) has been proposed ("Determining the Content of Hydrogen Dissolved in Quartz Glass Using the Methods of Raman Scattering and Mass Spectrometry"). The content of SiH groups is determined by means of Raman spectroscopy, wherein a calibration is carried out by means of a chemical reaction with hydrogen:
Si-O-Si + H 2 → Si-H + Si-OH, as described in Shelby "Reaction of hydrogen with hydroxyl-free vitreous silica" (J. Appl. Phys., Vol. 51, No. 5 (May 1980) , Pp. 2589-2593). The chlorine content of the silica glass is determined chemically by precipitation of chlorine as silver chloride or using an ion-selective electrode.

Die Inhomogenität des Brechungsindex Δn wird interferometrisch bei einer Wellenlänge von 633 nm (He-Ne-Laser) bestimmt, wobei sich Δn als Differenz zwischen dem Maximalwert und dem Minimalwert der Brechungsindexverteilung ergibt, gemessen über dem optisch genutzten Flächenbereich, auch CA Bereich ("clear aperture") genannt. Der CA Bereich ergibt sich durch Projektion des durchstrahlten Volumens auf eine Ebene senkrecht zur Durchstrahlungsrichtung.The inhomogeneity of the refractive index Δn becomes interferometric at a wavelength of 633 nm (He-Ne laser), where Δn is the difference between the maximum value and the Minimum value of the refractive index distribution, measured over the optically used surface area, also CA area ("clear aperture") called. The CA range is given by Projection of the irradiated volume on a plane perpendicular to the direction of transmission.

Die Spannungsdoppelbrechung wird interferometrisch bei einer Wellenlänge von 633 nm (He-Ne-Laser) nach der in "Measurement of the Residual Birefingence Distribution in Glass Laser Disk by Transverse Zeeman Laser" (Electronics and Communications in Japan, Part 2, Vol. 74, No. 5, 1991; (übersetzt aus Denshi Joho Tsushin Gakkai Ronbunshi Vol. 73-C-I, No. 10, 1990 pp. 652 - 657) beschriebenen Methode ermittelt. The stress birefringence is interferometrically at a wavelength of 633 nm (He-Ne laser) according to the "Measurement of the Residual Birefringence Distribution in Glass Laser Disk by Transverse Zeeman Laser "(Electronics and Communications in Japan, Part 2, Vol. No. 5, 1991; (translated from Denshi Joho Tsushin Gakkai Ronbunshi Vol. 73-C-I, No. 10, 1990) pp. 652-657).

Gegenüber den bisher in der Literatur beschriebenen und im Hinblick auf eine hohe Strahlenbeständigkeit gegenüber kurzwelliger UV-Strahlung ausgelegten Quarzglas-Qualitäten, zeichnet sich das Quarzglas, aus dem der erfindungsgemäße Rohling besteht unter anderem durch relativ hohe H2- und OH-Gehalte einerseits und durch einen Chlorgehalt mit einem vergleichsweise engen Konzentrationsbereich zwischen 60 Gew-ppm und 120 Gew-ppm andererseits aus.Compared with the previously described in the literature and with regard to a high radiation resistance to short-wave UV radiation designed quartz glass qualities, the quartz glass, from which the blank according to the invention consists, inter alia, by relatively high H 2 - and OH contents on the one hand and by a chlorine content with a comparatively narrow concentration range between 60 wt ppm and 120 wt ppm on the other hand.

Derartiges Quarzglas ist mittels des oben beschriebenen "Sootverfahrens" nicht ohne weiteres herstellbar. Denn beim Sootverfahren wird üblicherweise Quarzglas mit einem OH-Gehalt im Bereich einiger Gew-ppm- bis 200 Gew-ppm erhalten, wobei der H2-Gehalt infolge der Temperaturbehandlungen beim Verglasen und beim Homogenisieren des Quarzglases typischerweise unterhalb der Nachweisgrenze liegt. Demgegenüber sind für Quarzglas, das durch Direktverglasen hergestellt wird OH-Gehalte von 450 bis 1200 Gew.-ppm und H2-Gehalte um 1 x 1018 Moleküle/cm3 typisch. Es hat sich überraschend gezeigt, dass sich bei einem derartigen Quarzglas Chlor günstig auf die Strahlenbeständigkeit auswirkt, wenn das Chlor in einem engen Konzentrationsbereich zwischen 60 Gew-ppm bis 120 Gew-ppm vorliegt. Bei einem Chlorgehalt oberhalb von 120 Gew-ppm wird verstärkt induzierte Absorption aufgrund der Mitwirkung von Chlorradikalen bei der Defektzentrengeneration beobachtet (SiOSi + Cl* → SiCl+SiO*→(+H2+hv) SiOH+SiH+Cl*), während sich ein Chlorgehalt von weniger als 60 Gew-ppm ungünstig auf das Dekompaktierungsverhalten auswirkt.Such quartz glass is not easily produced by means of the "soot method" described above. For the soot method is usually quartz glass having an OH content in the range of a few ppm by weight to 200 ppm by weight, the H 2 content due to the temperature treatments during vitrification and homogenization of the quartz glass is typically below the detection limit. On the other hand, for quartz glass produced by direct glazing, OH contents of 450 to 1200 ppm by weight and H 2 contents of 1 x 10 18 molecules / cm 3 are typical. It has surprisingly been found that in such a quartz glass chlorine has a favorable effect on the radiation resistance, when the chlorine is present in a narrow concentration range between 60 ppm by weight to 120 ppm by weight. At a chlorine content above 120 ppm by weight, enhanced absorption due to the participation of chlorine radicals in the defect center generation is observed (SiOSi + Cl * → SiCl + SiO * → (+ H 2 + hv) SiOH + SiH + Cl *) while a chlorine content of less than 60 ppm by weight has an unfavorable effect on the decomposing behavior.

Es hat sich gezeigt, dass ein optisches Bauteil, das aus einem Quarzglas-Rohling mit den oben genannten Eigenschaften gefertigt wird, die Schädigungsmechanismen, die zu Kompaktierung und Dekompaktierung führen, vermieden oder zumindest deutlich reduziert sind. Brechzahländerungen im Verlauf des bestimmungsgemäßen Einsatzes deratiger Bauteile werden vollständig oder weitgehend vermieden, so dass die genannten Schädigungsmechanismen die Lebensdauer der aus dem erfindungsgemäßen Rohling gefertigten optischen Bauteile nicht begrenzen.It has been shown that an optical component consisting of a quartz glass blank with the top mentioned properties, the damage mechanisms leading to compaction and decompacting lead, avoided or at least significantly reduced. Refractive index changes in the course of the intended use deratiger components are completely or largely avoided, so that the damage mechanisms mentioned the life span the optical components made of the blank according to the invention do not limit.

Diese Wirkung der oben genannten Eigenschafts-Kombination auf das Schädigungsverhalten gegenüber kurzwelliger UV-Strahlung mit Energiedichten von mehr als 0,05 mJ/cm2 ist empirisch nachgewiesen worden, wie im Folgenden noch näher erläutert wird. Dabei hat sich außerdem gezeigt, dass bei derartigen Energiedichten OH-Gehalte von weniger als 500 Gew-ppm zu Kompaktierung führen. Quarzglas mit einem OH-Gehalt oberhalb von 1000 Gew-ppm zeigt eine stärkere Tendenz zu Dekompaktierung. This effect of the abovementioned property combination on the damage behavior with respect to short-wave UV radiation with energy densities of more than 0.05 mJ / cm 2 has been empirically demonstrated, as will be explained in more detail below. It has also been shown that at such energy densities OH contents of less than 500 ppm by weight lead to compaction. Quartz glass with an OH content above 1000 ppm by weight shows a stronger tendency to decompact.

Der zu RDP führende Schädigungsmechanismus wirkt sich bei H2-Gehalten von mehr als 2,0 x 1018 Molekülen/cm3 besonders deutlich aus. Wogegen bei einem H2-Gehalt von weniger als 3 x 1017 Molekülen/cm3 die oben erwähnte defektausheilende Wirkung von Wasserstoff gegenüber kurzwelliger UV-Strahlung mit Energiedichten von mehr als 0,05 mJ/cm2 so gering ist, dass es während des bestimmungsgemäßen Einsatzes des optischen Bauteils zu nicht tolerierbaren Transmissionsverlusten kommt.The RDP-leading damage mechanism is particularly pronounced at H 2 contents of more than 2.0 x 10 18 molecules / cm 3 . Whereas at an H 2 content of less than 3 x 10 17 molecules / cm 3, the above-mentioned defect-healing effect of hydrogen over short-wave UV radiation with energy densities of more than 0.05 mJ / cm 2 is so low that it is during the Proper use of the optical component to intolerable transmission losses comes.

Demgegenüber ist beim erfindungsgemäßen Rohling das Quarzglas sowohl im Hinbiick auf Kompaktierung als auch Dekompaktierung optimiert, und es weist gleichzeitig eine geringe induzierte Absorption gegenüber kurzwelliger UV-Strahlung auf.In contrast, the quartz glass in the blank according to the invention both in Hinbiick on Optimized compaction as well as decompaction, and at the same time it has a low induced Absorption against short-wave UV radiation.

Es hat sich als besonders günstig erwiesen, wenn der OH-Gehalt im Rohling im Bereich von 600 Gew-ppm bis 900 Gew-ppm, insbesondere im Bereich von 750 Gew-ppm bis 900 Gew-ppm liegt. Ein OH-Gehalt in diesem Bereich stellt einen bevorzugten Kompromiss zwischen Dekompaktierung und Kompaktierung einerseits und RDP andererseits dar, wenn das Quarzglas mit UV-Strahlung mit Energiedichten von mehr als 0,05 mJ/cm2 eingesetzt werden soll.It has proven to be particularly advantageous if the OH content in the blank in the range of 600 ppm by weight to 900 ppm by weight, in particular in the range of 750 ppm by weight to 900 ppm by weight. An OH content in this range represents a preferred compromise between decompaction and compaction on the one hand and RDP on the other hand, if the quartz glass is to be used with UV radiation with energy densities of more than 0.05 mJ / cm 2 .

Im Hinblick hierauf liegt der H2-Gehalt vorteilhafterweise im Bereich von 5 x 1017 Molekülen/cm3 bis 1 x 1018 Molekülen/cm3. Bei einem Quarzglas-Rohling mit einem H2-Gehalt in diesem Bereich ist sowohl die günstige, defektausheilende Wirkung des Wasserstoffs in besonders hohem Maße vorhanden, und es wird gleichzeitig Dekompaktierung weitgehend vermieden.In view of this, the H 2 content is advantageously in the range of 5 × 10 17 molecules / cm 3 to 1 × 10 18 molecules / cm 3 . In the case of a quartz glass blank having an H 2 content in this range, both the favorable, defect-curing effect of the hydrogen is present in a particularly high degree, and at the same time decompaction is largely avoided.

Vorzugsweise weist der Quarzglasrohling einen Chlorgehalt im Bereich von 80 Gew-ppm bis 100 Gew-ppm auf. Bei einem Chlorgehalt innerhalb dieses engen Konzentrationsbereichs wird insbesondere bei einem Einsatz des Quarzglas-Rohlings in Verbindung mit UV-Strahlung hoher Energiedichten von mehr als 0,05 mJ/cm2 eine geringe Dekompaktierung und induzierte Absorption erreicht.Preferably, the quartz glass blank has a chlorine content in the range of 80 ppm by weight to 100 ppm by weight. With a chlorine content within this narrow concentration range, a low decompaction and induced absorption is achieved, in particular when the quartz glass blank is used in conjunction with UV radiation of high energy densities of more than 0.05 mJ / cm 2 .

Hinsichtlich der Verwendung des Quarzglasrohlings wird die oben angegebene Aufgabe erfindungsgemäß dadurch gelöst, dass für einen Einsatz mit ultravioletter Strahlung einer vorgegebenen Pulsenergiedichte ε von mindestens 0,05 mJ/cm2 und für eine vorgegebene Pulszahl P ein Quarzglas ausgewählt wird, das einen Mindestwasserstoffgehalt CH2min und einen Maximalwasserstoffgehalt CH2max aufweist, die folgenden Bemessungsregeln genügen: GH2min [Moleküle/cm3 ] = 1,0 x 108 ε2 P und CH2max [Moleküle/cm3 ] = 2 x 1019 ε With regard to the use of the quartz glass blank, the above-mentioned object is achieved according to the invention by selecting a quartz glass which has a minimum hydrogen content C H2min for use with ultraviolet radiation of a predetermined pulse energy density ε of at least 0.05 mJ / cm 2 and for a predetermined pulse number P and a maximum hydrogen content C H2max , which satisfy the following design rules : G H2min [Molecules / cm 3 ] = 1.0 x 10 8th ε 2 P and C H2max [Molecules / cm 3 ] = 2 x 10 19 ε

Durch die Einstellung des Wasserstoffgehalts anhand der Bemessungsregeln (2) und (3) wird das Quarzglas hinsichtlich seines Schädigungsverhaltens gegenüber kurzwellliger UV-Strahlung weiter optimiert. Bemessungsregel (2) ergibt eine Mindestkonzentration an Wasserstoff in Abhängigkeit von den Bestrahlungsbedingungen (Pulsenergiedichte und Pulszahi) an, unterhalb von der die defektausheilende Wirkung von Wasserstoff so gering ist, dass es während des bestimmungsgemäßen Einsatzes des optischen Bauteils zu nicht tolerierbaren Transmissionsverlusten kommt. Bemessungsregel (3) hingegen definiert eine Obergrenze an Wasserstoff in Abhängigkeit von der Pulsenergiedichte, oberhalb der vermehrt RDP bzw. Dekompaktierung auftritt. Die angegebenen Wasserstoff-Konzentrationen beziehen sich jeweils auf den optisch genutzten Bereich innerhalb des Quarzglas-Rohlings (CA-Bereich). Üblicherweise handelt es sich dabei um den zentralen Bereich des Baueils bzw. des Quarzglas-Rohlings.By adjusting the hydrogen content according to the design rules (2) and (3) the quartz glass with respect to its damage behavior against short-wave UV radiation further optimized. Design rule (2) gives a minimum concentration of hydrogen depending on the irradiation conditions (pulse energy density and pulse rate), below which the defect-healing effect of hydrogen is so low that it is during the intended use of the optical component to intolerable Transmission losses comes. Dimensioning rule (3), on the other hand, defines an upper limit Hydrogen as a function of the pulse energy density, above the increased RDP or decompacting occurs. The indicated hydrogen concentrations refer in each case on the optically used area within the quartz glass blank (CA area). Usually this is the central area of the building part or of the quartz glass blank.

Vorzugsweise wird ein Quarzglas ausgewählt, das einen OH-Gehalt COH in einem Bereich aufweist, der folgender Bemessungsregel genügt: COH [Gew-ppm] = 1700 ε[mJ/cm2]0.4 ± 50 Preferably, a quartz glass is selected, which has an OH content C OH in a range which satisfies the following design rule: C OH [Wt ppm] = 1700 ε [mJ / cm 2 ] 0.4 ± 50

Im Idealfall tritt weder Kompaktierung noch Dekompaktierung auf. In der Praxis wird aber in Abhängigkeit von den Bestrahlungsbedingungen und den Quarzglas-Eigenschaften entweder Kompaktierung oder Dekompaktierung beobachtet. Es wurde überraschend gefunden, dass ein Quarzglas mit einem nach Bemessungsregel (4) ausgelegten OH-Gehalt dem genannten ldealfall nahe kommt, das heißt es zeigt weder eine auffällige Kompaktierung noch eine nennenswerte Dekompaktierung, , wenn es kurzwelliger UV-Strahlung einer Wellenlänge von < 250 nm mit einer Pulsenergiedichte ε von mehr als 0,05 mJ/cm2 ausgesetzt wird.Ideally, neither compaction nor decompaction occurs. In practice, however, either compaction or decompaction is observed, depending on the conditions of irradiation and quartz glass properties. It has surprisingly been found that a quartz glass with an OH content designed according to design rule (4) comes close to the ideal case mentioned, ie it shows neither a conspicuous compaction nor a significant decompaction, if short-wave UV radiation with a wavelength of <250 nm nm is exposed with a pulse energy density ε of more than 0.05 mJ / cm 2 .

Für eine Pulsenergiedichte im Bereiche der genannten Untergrenze ε = 0,05 mJ/cm2 ergibt die Bemessungsregel (4) einen OH-Gehalt von 513 Gew-ppm. For a pulse energy density in the range of the lower limit ε = 0.05 mJ / cm 2 , the design rule (4) gives an OH content of 513 ppm by weight.

Die Bemessungsregel (4) hat sich insbesondere für die Festlegung des OH-Gehalts im Hinblick auf geringe Kompaktierung und gleichzeitig geringe Dekompaktierung bewährt, wenn die Pulsenergiedichte kleiner als 0,3 mJ/cm2, vorzugsweise kleiner als 0,15 mJ/cm2, ist.The design rule (4) has proved to be particularly suitable for the determination of the OH content with regard to low compaction and at the same time low decompaction if the pulse energy density is less than 0.3 mJ / cm 2 , preferably less than 0.15 mJ / cm 2 , is.

Für den oberen Grenzwert ε = 0,3 mJ/cm2 ergibt sich dabei nach Bemessungsregel (4) ein OH-Gehalt zwischen 1000Gew-ppm und 1100 Gew-ppm.For the upper limit value ε = 0.3 mJ / cm 2 , an OH content of between 1000 μg-ppm and 1100 ppm by weight results according to design rule (4).

Nachfolgend wird die Erfindung anhand von Ausführungsbeispielen und anhand Zeichnung näher erläutert. Dabei zeigt

Figur 1
ein Diagramm zur Erläuterung des Auftretens von Kompaktierung oder Dekompaktierung in Abhängigkeit vom OH-Gehalt des Quarzglases und der Pulsenergiedichte der Strahlung.
The invention will be explained in more detail by means of embodiments and with reference to the drawing. It shows
FIG. 1
a diagram for explaining the occurrence of compaction or decompaction in dependence on the OH content of the quartz glass and the pulse energy density of the radiation.

Bei dem Diagramm in Figur 1 ist der OH-Gehalt COH in Gew-ppm (in der Figur angegeben als "OH content") gegen die Pulsenergiedichte ε in mJ/cm2 (in der Figur angegeben als "energy density") aufgetragen. Die eingezeichnete Kurve beruht auf Schädigungsmessungen bei verschiedenen Quarzglas-Qualitäten, die sich in ihrem OH-Gehalt unterscheiden. Die Messung erfolgt unter Laserstrahlung einer Wellenlänge von 193 nm und bei einer Laserpulslänge zwischen 20 und 50 Nanosekunden. Die Laserpulslänge wird nach der in V. Liberman, M. Rothschild, J.H.C. Sedlacek, R.S. Uttaro, A. Grenville "Excimer-laser-induced densification of fused silica: laser-fluence and material-grade effects on scaling law", Journal Non-Cryst.Solids 244 (1999) S.159-171 beschriebenen Methode bestimmt.
Die unter den vorgenannten Bedingungen ermittelten Messwerte sind als Rauten dargestellt. Die Kurve repräsentiert diejenigen COH/ε-Paare, bei denen weder Kompaktierung noch Dekompaktierung beobachtet wird. Der Bereich (1) oberhalb der Kurve kennzeichnet den Bereich, in dem Kompaktierung auftritt, und der Bereich (2) unterhalb der Kurve kennzeichnet den Bereich, in dem Dekompaktierung auftritt.In the diagram in FIG. 1 , the OH content C OH in ppm by weight (indicated in the figure as "OH content") is plotted against the pulse energy density ε in mJ / cm 2 (indicated in the figure as "energy density"). The drawn curve is based on damage measurements with different qualities of quartz glass, which differ in their OH content. The measurement takes place under laser radiation of a wavelength of 193 nm and at a laser pulse length between 20 and 50 nanoseconds. The laser pulse length is determined according to V. Liberman, M. Rothschild, JHC Sedlacek, RS Uttaro, A. Grenville, "Excimer-laser-induced densification of fused silica: laser-fluence and material-grade effects on scaling law", Journal Non- Cryst. Solids 244 (1999) p.159-171.
The measured values determined under the aforementioned conditions are shown as diamonds. The curve represents those C OH / ε pairs where neither compaction nor decompaction is observed. The area (1) above the curve indicates the area in which compaction occurs, and the area (2) below the curve indicates the area in which decompaction occurs.

Der Verlauf der Kurve lässt sich durch die Formel (4): COH [Gew-ppm] = 1700 · ε [mJ/cm2]0.4 ± 50 annähernd beschreiben. The course of the curve can be defined by the formula (4): C OH [Wt ppm] = 1700 · ε [mJ / cm 2 ] 0.4 ± 50 approximately describe.

Anhand der Kurve oder der Formel (4) kann somit für jede Pulsenergiedichte zwischen 0,05 und 0,3 mJ/cm2 der OH-Gehalt ausgewählt werden, den ein Quarzglas aufweisen muss, damit es weder Kompaktierung noch Dekompaktierung zeigt.Thus, for each pulse energy density between 0.05 and 0.3 mJ / cm 2, the OH content which a quartz glass must have, so that it exhibits neither compaction nor decompaction, can be selected from the curve or formula (4).

Beispiele für derartige Quarzgläser und Vergleichsbeispiele dazu zeigt Tabelle 1.

Figure 00110001
Examples of such quartz glasses and comparative examples thereof are shown in Table 1.
Figure 00110001

Tabelle 1 zeigt die Ergebnisse von Bestrahlungsmessungen an Quarzglas-Rohlingen unterschiedlicher chemischer Zusammensetzung und bei verschiedenen Bestrahlungsbedingungen. In den drei letzten Spalten der Tabelle ist qualitativ angegeben, ob der jeweilige Rohling Kompaktierung, Dekompaktierung oder induzierte Absorption zeigt.Table 1 shows the results of irradiation measurements on quartz glass blanks different chemical composition and under different irradiation conditions. In the last three columns of the table is given qualitatively, whether the respective blank compacting, Decompacting or induced absorption shows.

Die in den Spalten 2 bis 8 genannten Eigenschaften werden jeweils an einem zylinderförmigen Quarzglasrohling mit einem Außendurchmesser von 240 mm und einer Dicke von 60 mm ermittelt. Es handelt sich dabei um Rohlinge für Linsen für ein Mikrolithographiegerät, das mit Excimer-Laserstrahlung mit einer Wellenlänge von 193 nm arbeitet. Abgesehen von einem geringen Übermaß, das bei der Fertigung der Linse noch abgetragen wird, entsprechen die Rohling-Abmessungen auch den Linsenabmessungen. Das dem CA-Bereich der daraus erhaltenen Linse entsprechende Quarzglas-Volumen wird hier durch die Kreisfläche der Linse - abzüglich eines Randes von wenigen Millimetern für die Linsenfassung - und der Dicke bestimmt. In der Spalte "O±" von Tabelle 1 ist die Sauerstoffdefektstellen-Konzentration angegeben, in der Spalte "Δn" die über den CA-Bereich ermittelte Brechungsindexdifferenz, und in der Spalte "Λ" die im CA-Bereich ermittelte maximale Doppelbrechung.The properties mentioned in columns 2 to 8 are each determined on a cylindrical quartz glass blank having an outer diameter of 240 mm and a thickness of 60 mm. These are lens blanks for a microlithography device that uses excimer laser radiation with a wavelength of 193 nm. Apart from a small excess, which is still removed in the manufacture of the lens, the blank dimensions also correspond to the lens dimensions. The quartz glass volume corresponding to the CA region of the lens obtained therefrom is determined here by the circular area of the lens, minus an edge of a few millimeters for the lens frame, and the thickness. In the column "O ± " of Table 1, the oxygen defect site concentration is indicated, in the column "Δn" the refractive index difference determined over the CA region, and in the column "Λ" the maximum birefringence determined in the CA region.

Zur Durchführung der Bestrahlungsversuche wurden aus den jeweiligen Quarzglas-Rohlingen stabförmige Proben mit einer Abmessung von 25 x 25 x 200 mm3 entnommen und in gleicher Art und Weise vorbereitet (Politur der gegenüberliegenden 25 x 25 mm2 -Flächen).To carry out the irradiation experiments, rod-shaped samples with a dimension of 25 × 25 × 200 mm 3 were removed from the respective quartz glass blanks and prepared in the same manner (polishing of the opposite 25 × 25 mm 2 surfaces).

Zur Klärung des Schädigungsverhaltens der Proben hinsichtlich Kompaktierung oder Dekompaktierung wurden die Proben mit UV-Strahlung einer Wellenlänge von 193 nm bestrahlt, wobei die Pulsenergiedichte variiert wurde, wie in Spalte 8 von Tabelle 1 angegeben. Die Pulszahl bei diesen Bestrahlungsversuche betrug jeweils 5 Milliarden.To clarify the damage behavior of the samples with regard to compaction or decompaction The samples were irradiated with UV radiation of a wavelength of 193 nm, wherein the pulse energy density was varied as indicated in column 8 of Table 1. The pulse rate at These irradiation attempts amounted to 5 billion each.

In der Spalte "Induzierte Absorption" sind zwei Schädigungsmechanismen zusammengefasst, die sich in einem Anstieg der Absorption äußern, nämlich die lineare Absorptionszunahme und der eingangs beschriebene RDP. Zur Klärung des Schädigungsverhaltens der Proben hinsichtlich induzierter Absorption wurden die Proben ebenfalls mit UV-Strahlung einer Wellenlänge von 193 nm und mit der in Spalte 8 genannten Pulsenergiedichte bestrahlt. Zur Feststellung des RDPs genügt eine Pulszahl von 1 Million Pulsen, während für die Ermittlung der linearen Absorptionszunahme eine Pulszahl von mindestens 1 Milliarde Pulsen erforderlich ist. Hierzu wird der Transmissionsverlust der Probe bestimmt, indem während der Bestrahlung die Intensitätsabnahme des verwendeten Laserstrahls nach Durchgang durch die Probe bestimmt wird.In the column "induced absorption" two damage mechanisms are summarized, which express themselves in an increase in absorption, namely the linear absorption increase and the RDP described above. To clarify the damage behavior of the samples with regard to induced absorption, the samples were also exposed to UV radiation of one wavelength of 193 nm and irradiated with the pulse energy density mentioned in column 8. To establish the RDPs will suffice for a pulse count of 1 million pulses, while for the determination of the linear absorption increase a pulse rate of at least 1 billion pulses is required. For this purpose is the transmission loss of the sample is determined by reducing the intensity during irradiation the laser beam used is determined after passage through the sample.

Nach den Bestrahlungsversuchen wurden Kompaktierung und Dekompaktierung bestimmt, indem mit einem handelsüblichen Interferometer (Zygo GPI-XP) bei einer Wellenlänge von 633nm, die relative Zunahme bzw. Abnahme der Brechzahl im bestrahlten Bereich im Vergleich zum unbestrahlten Bereich gemessen wurde.After irradiation experiments, compaction and decompaction were determined by with a commercial interferometer (Zygo GPI-XP) at a wavelength of 633nm, the relative increase or decrease of the refractive index in the irradiated area in comparison to the unirradiated area was measured.

Die Quarzglas-Rohlinge sind zur Herstellung von optischen Linsen für ein Mikrolithographiegerät für einen Einsatz mit UV-Strahlung einer Wellenlänge von 193 nm ausgelegt, wobei das optische Bauteil im Verlauf seines bestimmungsgemäßen Einsatzes typischerweise einer Strahlung mit einer Energiedichte von etwa 0,1 mJ/cm2 ausgesetzt wird. Typische Pulszahlen liegen zwischen 1011 und 1012.The quartz glass blanks are designed for the production of optical lenses for a microlithography device for use with UV radiation of a wavelength of 193 nm, wherein the optical component during its intended use typically a radiation having an energy density of about 0.1 mJ / cm 2 is suspended. Typical pulse numbers are between 10 11 and 10 12 .

Die Rohlinge 1 bis 4 gemäß Tabelle 1 wurden folgendermaßen hergestellt:
Es handelt sich um nach dem Direktverglasungsverfahren hergestellte Quarzgläser. Auf einem scheibenförmigen, um seine Mittelachse rotierenden Substrat wird mittels eines Knallgasbrenners feinteiliges SiO2 abgeschieden, das unmittelbar durch die Hitze der Knallgasflamme unter Bildung eines stabförmigen Quarzglasrohlings verglast wird. Der Wasserstoffgehalt liegt in diesem Verfahrensstufe noch bei etwa 2 x 1018 Molekülen/cm3.Blanks 1 to 4 according to Table 1 were prepared as follows:
These are quartz glasses produced by the direct glazing process. On a disc-shaped, rotating about its central axis substrate is finely divided SiO 2 by means of a detonating gas burner, which is directly vitrified by the heat of the oxyhydrogen flame to form a rod-shaped quartz glass blank. The hydrogen content in this process stage is still about 2 × 10 18 molecules / cm 3 .

Wie aus Tabelle 1 ersichtlich, unterscheiden sich die Rohlinge 1 bis 4 lediglich in den jeweiligen Chlorgehalten. Der CI-Gehalt wird durch Vorgabe der Flußraten für H2, O2 und SiCl4 eingestellt.As can be seen from Table 1, the blanks 1 to 4 differ only in the respective chlorine contents. The CI content is adjusted by setting the flow rates for H 2 , O 2 and SiCl 4 .

Außerdem wird anhand Bemessungsregel (4) der OH-Gehalt festgelegt, der in Verbindung mit der typischen Einsatz-Pulsenergiedichte von etwa 0,1 mJ/cm2 einzustellen ist. Die Einstellung des OH Gehalts erfolgt ebenfalls über die Flußraten der Einzelmedien (H2, O2 und SiCl4). Dadurch ergibt sich ein OH-Gehalt von etwa 700 Gew-ppm, der somit innerhalb des Bereiches liegt, der durch Bemessungsregel (4) für ε = 0,1 mJ/cm2 folgendermaßen spezifiziert ist: COH [Gew-ppm] = 1700 · ε [mJ/cm2]0,4   ± 50   → 677 ± 50 Gew-ppm In addition, design rule (4) sets the OH content to be set in conjunction with the typical feed pulse energy density of about 0.1 mJ / cm 2 . The OH content is also adjusted via the flow rates of the individual media (H 2 , O 2 and SiCl 4 ). This results in an OH content of about 700 ppm by weight, which is thus within the range specified by design rule (4) for ε = 0.1 mJ / cm 2 as follows: C OH [Wt ppm] = 1700 · ε [mJ / cm 2 ] 0.4 ± 50 → 677 ± 50 wppm

Weiterhin wird der Wasserstoffgehalt anhand den Bemessungsregeln (2) und (3) festgelegt, wie er in Verbindung mit der typischen Einsatz-Pulsenergiedichte von etwa 0,1 mJ/cm2 einzustellen ist. Die Einstellung des vorgegebenen H2-Gehalts erfolgt durch Tempern der Rohlinge bei 1100°C.Furthermore, the hydrogen content is determined by the design rules (2) and (3), as it is to be set in connection with the typical application pulse energy density of about 0.1 mJ / cm 2 . The setting of the predetermined H 2 content is carried out by annealing the blanks at 1100 ° C.

Dadurch ergibt sich ein H2-Gehalt von 1,4 x 1018 Molekülen/cm3, der damit unter Berücksichtigung der Ausdiffusion während der Temperung des heißverformten Linsenrohlings (s.u.) (H2 Verlust durch Ausdiffusion ca. 30%) innerhalb der Grenzen CH2min und CH2max liegt, die durch die Bemessungsregeln (2) und (3) für ε = 0,1 mJ/cm2 folgendermaßen spezifiziert sind: CH2min [Moleküle/cm3] = 1,0 x 108 (0,1)2 P CH2max [Moleküle/cm3] = 2 x 1019 (0,1) This results in an H 2 content of 1.4 × 10 18 molecules / cm 3 , thus taking into account the outdiffusion during the annealing of the hot-formed lens blank (see below) (H 2 loss by outdiffusion about 30%) within the limits C H2min and C H2max , which are specified by the design rules (2) and (3) for ε = 0.1 mJ / cm 2 as follows: C H2min [Molecules / cm 3 ] = 1.0 x 10 8th (0.1) 2 P C H2max [Molecules / cm 3 ] = 2 x 10 19 (0.1)

Mit ε = 0,1 mJ/cm2ergibt sich nach dieser Bemessungsregel ein im Quarzglas einzustellender minimaler H2-Gehalt, je nach Pulszahl zwischen 1 x 1017 Molekülen/cm3 und 10 x 1017 Molekülen/cm3 - und ein maximaler H2-Gehalt von 2 x 1018 Molekülen/cm3.With ε = 0.1 mJ / cm 2 , this rule of thumb gives a minimum H 2 content to be set in the quartz glass, depending on the number of pulses between 1 × 10 17 molecules / cm 3 and 10 × 10 17 molecules / cm 3 - and a maximum H 2 content of 2 × 10 18 molecules / cm 3 .

Zum Homogenisieren wird der Quarzglasrohling anschließend in eine Quarzglas-Drehbank eingespannt, zonenweise auf eine Temperatur von ca. 2000 °C erhitzt und dabei verdrillt. Ein dafür geeignetes Homogenisierungsverfahren ist in der EP-A1 673 888 beschrieben. Nach mehrmaligem Verdrillen liegt ein Quarzglaskörper in Form eines Rundstabes mit einem Durchmesser von 80 mm und einer Länge von ca. 800 mm vor, der in drei Richtungen schlierenfrei ist.For homogenizing the quartz glass blank is then clamped in a quartz glass lathe, heated zone by zone to a temperature of about 2000 ° C and thereby twisted. One for that suitable homogenization method is described in EP-A1 673 888. After several times Twisting is a quartz glass body in the form of a round rod with a diameter of 80 mm and a length of about 800 mm, which is free of streaks in three directions.

Durch eine Heißverformung bei einer Temperatur von 1700 °C und unter Verwendung einer stickstoffgespülten Schmelzform wird daraus ein kreisrunder Quarzglaszylinder mit einem Außendurchmesser von 240 mm und einer Länge von 80 mm gebildet. Nach einem weiteren Tempervorgang, bei der der Quarzglaszylinder unter Luft und Atmosphärendruck auf 1100 °C erhitzt und anschließend mit einer Abkühlrate von 2°C/h auf 900°C abgekühlt wird, wird lediglich noch (im CA-Bereich) eine Spannungsdoppelbrechung von maximal 2 nm/cm gemessen, und die Brechzahlverteilung ist derart homogen, dass der Unterschied zwischen dem Maximalwert und dem Minimalwert unterhalb von 2 x 10-6 liegt. Aus den zentralen Bereich des Rohlings wird eine stabförmige Probe mit einer Abmessung von 25 x 25 x 200 mm3 entnommen, die einen H2 Gehalt von ca. 1 x 1018 Molekülen/cm3 und ca. 700 Gew-ppm OH aufweist. Die Herstellung der Rohlinge 5 bis 7 erfolgt wie die der Rohlinge 1-4 durch Variation der Flußraten der Einzelmedien. Der H2-Gehalt der erhaltenen Rohlinge wird durch Wahl der Länge des Temperprogramms und unter Berücksichtigung der Diffusion der Temperung des heißverformten Quarzglaszylinders eingestellt.By hot deformation at a temperature of 1700 ° C and using a nitrogen-purged melt mold, a circular quartz glass cylinder having an outer diameter of 240 mm and a length of 80 mm is formed therefrom. After a further tempering process in which the quartz glass cylinder is heated to 1100 ° C. under air and atmospheric pressure and then cooled to 900 ° C. at a cooling rate of 2 ° C./h, only (in the CA range) a stress birefringence of not more than 2 is obtained nm / cm, and the refractive index distribution is so homogeneous that the difference between the maximum value and the minimum value is less than 2 × 10 -6 . From the central region of the blank, a rod-shaped sample with a dimension of 25 × 25 × 200 mm 3 is taken, which has an H 2 content of about 1 × 10 18 molecules / cm 3 and about 700 ppm by weight OH. The production of the blanks 5 to 7 takes place as that of the blanks 1-4 by varying the flow rates of the individual media. The H 2 content of the resulting blanks is adjusted by selecting the length of the annealing program and taking into account the diffusion of the annealing of the hot-formed quartz glass cylinder.

• Ergebnisbewertung• Evaluation of results

Hinsichtlich des Auftretens von Kompaktierung, Dekompaktierung und induzierter Absorption gemäß Tabelle 1 zeigen die Rohlinge 1, 5 und 7 bei Energiedichten von 0,1 0,2 bzw. 0,05 mJ/cm2 die besten Ergebnisse. Rohling 2 zeigt unter Einwirkung von ultravioletter Strahlung mit einer relativ hohen Energiedichte von 0,3 mJ/cm2 Kompaktierung, was je nach Anwendungsfall in Grenzen tolerierbar sein kann.With regard to the occurrence of compaction, decompaction and induced absorption according to Table 1, the blanks 1, 5 and 7 show the best results at energy densities of 0.1 0.2 and 0.05 mJ / cm 2, respectively. Blank 2 shows under the action of ultraviolet radiation with a relatively high energy density of 0.3 mJ / cm 2 compaction, which depending on the application can be tolerated within limits.

Claims (7)

  1. A quartz glass blank for an optical component for transmitting ultraviolet radiation of a wavelength of 250 nm and shorter with a glass structure essentially without oxygen defects, an H2 content ranging from 3 x 1017 molecules/cm3 to 2.0 to 1018 molecules/cm3, an OH content ranging from 500 wt ppm to 1000 wt ppm, a content of SiH groups of less than 2 x 1017 molecutes/cm3, a chlorine content ranging from 60 wt ppm to 120 wt ppm, an inhomogeneity in the refractive index Δn of less than 2 ppm and a strain birefringence of less than 2 nm/cm.
  2. A quartz glass blank as claimed in claim 1, characterized in that the OH content is within the range of 600 wt ppm to 900 wt ppm, preferably within the range of 750 wt ppm to 900 wt ppm.
  3. A quartz glass blank as claimed in claim 1 or 2, characterized in that the H2 content is within the range of 5 x 1017 molecules/cm3 to 1 x 1018 molecules/cm3.
  4. The quartz glass blank according to claim 1, characterized in that the quartz glass blank has a chlorine content ranging from 80 wt ppm to 100 wt ppm.
  5. Use of a quartz glass blank as claimed in any one of claims 1 to 4 for a component for use in microlithography in combination with ultraviolet radiation of a wavelength of 250 nm and shorter, characterized in that for an application with ultraviolet radiation of a predetermined pulse energy density ε of at least 0.05 mJ/cm2 and for a predetermined pulse number P, a quartz glass is selected that has a minimum hydrogen content CH2min and a maximum hydrogen content CH2max satisfying the following dimensioning rules: CH2min [molecules/cm3] = 1.0 x 108 ε2 P and CH2max [molecules/cm3] = 2 x 1019 ε
  6. Use of a quartz glass blank as claimed in claim 5, characterized in that a quartz glass is selected that has an OH content COH within a range satisfying the following dimensioning rule: COH [wt ppm] = 1700 · ε [mJ/cm2]0.4   ± 50
  7. Use of a quartz glass blank as claimed in claim 5, characterized in that the pulse energy density ε is less than 0.3 mJ/cm2, particularly less than 0.15 mJ/cm2.
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US20030119652A1 (en) 2003-06-26
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US7064093B2 (en) 2006-06-20
JP2003183037A (en) 2003-07-03
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DE50201208D1 (en) 2004-11-11
JP4437886B2 (en) 2010-03-24

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